Process for producing oil shale in situ by electrocarbonization



Oct. 8, 1963 H. w. PARKER 3,106,244

`PROCESS FOR PRODUCING OIL SHALE IN SITU BY ELECTROCARBONIZATION FiledJune 20, 1960 2 Sheets-Sheet 1 28 lNJBrloN PRODUCTION D-Q30 AIRPRODUCTION INJECTION INJACIION 28 PRODUCTION 243 .Z( LDq-@BO INVENTOR.H.W. PARKER BY g A T7' ORNE YS O.- 8, 1963 H. w. PARKER 3,106,244

PROCESS FOR PRODUCING OIL SHALE IN SITU BY ELECTROCARBONIZATION FiledJune 20, 1960 2 Sheets-Sheet 2 32 AIR OR 2e STEAM SHALE oll.

4 AND GASES OXIDIZING PRODUCTION GAS F/G.5 I4 INVENTOR. 15 H. w. PARKERA TTORNE Ys United States Patent O 3,105,244 PRCESS FR PRDDUCNG @ILSi-IALE IN SlTU BY ELECTROCARBONIZATIN Harry W. Parker, Bartlesville,Gkla., assigner to Phillips Petroleum Company, a corporation of DelawareFiled June 20, 1960, Ser. No. 37,451 11 Claims. (Cl. 16S-11) Thisinvention relates to Van improved process for producing oil shale insitu.

The production of oil from oil shale without removing the shale from thedeposit is rendered difficult by the impermeable `character of theshale. This is particularly true with reference to recovery of the oilby in lsitu combustion or other heating processes. One method ofproducing oil shale in situ is disclosed in my copending applicationS.N. l27,627, hled May 9, 1960, wherein electrocarbonization of theshale is utilized as a means of distilling hydrocarbons from the shalebed. This invention is concerned with an extension and modiication ofthe electrocarbonization process disclosed in said application.

Accordingly, it is an object of the invention to provide an improvedprocess for producing oil from oil shale in situ. Another object is toprovide an improved process for producing shale by electrocarbonizationand in situ combustion. A yfurther object is to provide a method ofextending the zone in which electrocarbonization is effected whenutilizing this method for the in situ production of oil shale. Otherobjects of the invention will become apparent to one skilled in the artupon consideration of the accompanying disclosure.

In accordance with one aspect of the invention, a substantial section ofa shale bed is electrocarbonized around a production well therein so asto distill hydrocarbons therefrom and produce hot permeable coke thereinat combustion supporting temperature; thereafter afree-oxygen-containingV gas is injected into an offset injection wellfrom which fractures lead to the carbonized section so that the injectedgas passes into the hot section thereby igniting the hot carbon; thecombustion is continued by continuing the injection `of said gas; andthe lluids produced by lthe electrocarbonizing step and the combustionstep are recovered thru the production well. In this process the shalesurrounding the electrocarbonized section radially outwardly therefromis radially fractured by the expansion of said section during theelectrocarbonizing step.

The method of effecting the electrocarbonizaltion step is disclosed inthe above-identified copending application and comprises, broadly,positioning a pair of electrodes in a well in contact with the shale andinsulated from each other except thru the shale, and passing currentthru the shale Ibetween the electrodes by establishing sufficiently highvoltage potential across the electrodes. Broadly, this method is welldefined in the prior art as applied to carbonaceous deposits containinga conducting medium, such as salt water.

One embodiment of the invention comprises injecting the (D2-containinggas thru the injection well at suicient concentration and rate to movethe combustion front established in the permeable coke at the outerperiphery of the coked section to the wall of the production Well. Thisburns out the coke from the permeable area and renders the burned outarea electrically non-conductive so that reestablishment of a highpotential difference across the electrodes forces a current to flow thmthe shale more remote from the production well and thru the shalesurrounding the previously coked section. This has the effect ofexpanding the produced and coked zone farther into the sha-le from theproduc- 3,1%,244 Patented Get. 1963 tion well. In order to facilitatecurrent flow across the fractures, particulate conductive media, such ascopper, iron, alumina, etc., may be injected with a suitable fluid.

Another embodiment of the invention comprises injecting Oz-containinggas thru either the injection well or the production well so as toignite the coke in the electrocarbonized section and move a combustionzione or front thru the coke into the shale adjacent the fracturesleading to the injection well, thereby producing hydrocarbons from theshale `adjacent the fractures. After the shale is burned in this mannerand the unproduced shale deeper in the stratum from the fractures isheated to elevated temperatures, further electrocarbonization is readilyeffected by placing one of the electrodes in the injection well incontact with the shale and flowing current thru the hot shale from onewell to the other. This me-thod produces additional oil from the shaleand can be followed by another burning step. This additional burningstep is effected by injecting OZ-containing gas into the shalefromeither one of the we-lls and producing from the other.

A further embodiment of the invention comprises injecting particulateIsolid conductive material such as particles o-f metal, graphite, iron,zinc, magnesium, aluminum, etc., into the fractures between the wellsafter the electrocarbonizat-ion step, and placing one of the electrodesin the injection Well. The establishment o-f high potential between theelectrodes now has the effect o-f passing current thru the fracturesfrom conductive particle to conductive particle, thereby heating theadjacent shale so as to render the same conductive. Continued passage ofcurrent electrocarbonizes the shale adjacent the fractures and distillshydrocarbon material therefrom. This step is then followed by acombustion step effected by injecting O2-containing gas thru either oneof the wells and producing thru the other. After the coke is burned outin this manner, further electrocarbonizing is effected in the hot shaleadjacent the denuded area.

Another material which can be utilized in the process to make itpossible to pass current thru the fractures comprises a slurry of carbonparticles in brine. "It is helpful to incorporate in the brine adissolved organic compound which is carbonizable, such as sugar ormolasses. Graphite powder wet with oil is also a successful conductingmaterial for electrocarbonizing in the fractures.

-In shale beds in which the fracturing due to swelling 0f theelectrocarbonized section around the production well is of such smallmagnitude as to render operation difcult, it is feasible to artificiallyfracture the intervening shale between the injection wel-l, or aplurality of wells in a ring around the production well, and theproduction well so that the fractures formed by the electrocarbonizationare expanded and/or new fractures are formed extending from theinjection wells into the eleotrocarbonized section.

A more complete understanding of the invention may be had by referenceto the accompanying schematic drawing of which yFIGURE l is a verticalsection thm an oil shale bed showing an arrangement of apparatus foreffecting one embodiment of the invention; FIG- UREZ is a similar viewshowing another arrangement of apparatus; FIGURE 3 is a similar viewshowing a further arrangement of apparatus `for effecting anotherembodiment of the invention; lFIGURE 4 is a similar View showing aontherembodiment of the invention; and FIGURE 5 is a plan view of a wellpattern useful in effecting the invention.

Referring to FIGURE l, a subterranean shale bed lll is penetrated bywells 12 and 14 closely spaced therein (about to 5G feet). he wells areprovided with casings 1o and 1S extending substantially to the upperlevel of the shale. Casing is provided with well head 2G thru whichtubing 22 extends. An air injection conduit 214 passes thru the upperend of the casing. Casing 1S is provided with weil head 26 thru whichtubing 28 extends and the conduit 31B passes thru the upper end of thecasing. Conduits 23 and 31? provide air injection and product takeoffmeans. Casing 15 is connected by lead line 32 to generator 33 or otherpower source to serve as one electrode, and electrode 34, positioned inwell 12 in contact with a shale or with conductive material forming apath to 'the shale, is connected by lead 36 with generator 33.

In operation with the arrangement shown in FIG- URE l, the shaleadjacent Well 12 is heated by any suitable means so that it becomesconductive and a high potential is established between casing 16 andelectrode 34 so as to heat the intervening shale and distillhydrocarbons therefrom. In instances in which the shale ccntainssuiicient electrolyte (salt water), or is otherwise conductive, thepreliminary heating step may be omitted. In most instances shales aresubstantially dry and nonconductive and the heating step is essentialbefore the shale `intermediate the electrodes can be eiectrocarbonized.In dry `oil shale, the method of my above-identi .fied application maybe utilized to provide the essential heat step. This method comprisespacking well 12 between electrode 34 and the lower end of casing 16 witha conductive material in particulate form and placing at an intermediatelevel therein a high resistance section which melts after the heatingstep has continued sufficiently to heat the wall of the well, therebycutting oif ow thru the conductive material and requiringr the currentto flow thru the shale at the periphery of the well. The conductivematerial may comprise iron filings or steel wool on which copper sulfatesolution has been flushed, or [steel wool wet with graphite brine paste.In this type of operation it is essential to insulate lead 36 from theconductive packing material.

After the heating step has been effected, the electrocarbonization ofthe shale around well 12 is commenced and continued until a substantialsection 42 bounded by lines 38 has been carbonized and renderedpermeable. During the electrocarbonizaticn step, fractures 40 areextended radially outwardly from the carbonized section 42. This iscaused by the swelling of section 42 during the electrocarbonizing step.Fractures 40 include both vertical and horizontal fractures. Well 14 iswithin the pattern of fractures 40 surrounding well `12 Aand this opensup the formation to well 14 so that injection of air thru either well 12or well 14 forces air thru the shale via the fractures to the oppositewell. By injecting air thru well 14 at -a suflicient rate, a combustion`front or zone is established in section 42 in the hot coke therein andthe front is moved by inverse drive to well 14 with production beingrecovered thru `well 12.

By injecting air or other Ogicontaining gas such as diiuted air,oxygen-enriched air, or pure oxygen, thru well .12 into the hot coke insection 42, a direct drive combustion front is established `and movedthru the shale via the fractures to well 14 from which the producedfluids are recovered in conventional manner thru tubing 28 or line 30.

Referring to FIGURE 2, the arrangement shown therein is similar to thatof FIGURE l, but in addition to the electrodes in well 12, an additionalelectrode 50 is positioned in well 14 and connected by lead 53 with thesame lead from generator 33 as connects with lend 36. Switches 54 and 56are provided for changing the voltage application from electrode 34 toelectrode 5t). The arrangement shown in FIGURE 2 is intended to beutilized after the electrocarbonization step and the in situ combustionstep described in rel-ation to FIGURE l have taken place. The in situcombustion step burns hydrocarbon in the 4 shale and distills additionalhydrocarbon along the fractures so as to heat the unprcduced shalebetween the fractures sufliciently high to render electrocarbonizationeffective when high potential is applied to electrodes 16 and 5t). Inthis manner additional oil is distilled from the shale to increase theproduction therefrom.

Referring now to FIGURE 3, electrode 58 comprises a tubing stringextending substantially to the bottom of the shale bed. The lowersection of the well is packed around tubing 5S with a conductivematerial 66 so that by application of high voltage to electrodes 16 and553 the surrounding shale is electrocarbonized to 'for-rn a porous hotcoked section of shale 42. In order to drive the produced yand cokedsection 42 farther into the shale, a fracture system is established fromWell 14 to section 42 as by placing packers 62 and 64 in well 14 andexerting fluid fracturing pressure thru tubing 28. Fracturing system 66is thus formed extending from well 14 to Iwell 12, .preferably after theelectrocanbonizing step or during the final phase thereof. While thecoke in section 42 is at cornbustion supporting temperature, air isinjected thru tubing 28 and thru fracture system 66 into the hot coke ata relatively slow rate so that a direct drive combustion zone is movedfrom the outer periphery of the hot coke to the wall of well 12, therebyproducing a clean, :burnedout section of shale 63 within section 42. Adirect drive combustion zone always burns the formation clean so that itis no longer a conducting medium for an electric current. Now, by againestablishing a lhigh potential between electrcdes 16 and 53 the currentis forced to flow therebetween around coked section 42 because of thenon-conducting section 68. In this manner electrocarbonization of anadditional outer section 70 of the shale bed is produced and coked. Thisoperation can be repeated `by again propagating a direct drivecombustion front from the outer boundary of the coked section 70 alongthe fracture to the previously denuded section 68.

Another embodiment of the invention effective with the arrangement shownin FIGURE 2, comprises injecting solid particulate yconductive material,such as metal tilings, into the fracture system 40 extending from well14 to woll 12 so that a conductive passageway is provided along thefractures to burned and carbonized section 42. By applying highpotential 'across electrodes 34 and Si) the shale adjacent the fracturesis heated to distill hydrocarbons therefrom, leaving a hot cc-kedresidue in the shale which is permeable and amenable to in situcombustion to further heat the intervening shale. Here again, alternatecombustion and electrocarbonization is effected in producing ,theremaining carbonaceous material in the shale between wells 12 and 14.

The direction of moving the combustion front when injecting O2containinggas thru well 14 with the arrangement shown in FIGURE 3 is determined bythe rate at which the gas is injected and/ or by the composition (O2content) of the gas. High ilow rates, usually 20 standard cubic lfeetper hour per square feet cross sectional area of the front, produceinverse or countercurrent drive of the front. At lower rates of airinjection, the resulting drive is direct (concurrent). The direct driveof the front is also effected by reducing the O2 concentration in theinjected gas as by diluting air with combustion gas. Increasing the O2concentration in the injected gas above the normal 2O volume percentfavors inverse movement of the front. A combination of these .twofactors, viz., injecting rate and O2 concentration, can be utilized tocontrol the direction of the fron-t movement. A convenient method ofmoving the front from the outer periphery of the coked section 42 towell 12 is to inject an admixture of air and steam such as an admixturecontaining from 10 to 50 volume percent steam. Steam in adrniXture withair burns the hot coke yand effects the water gas reaction.

FiGURE 4 shows the stratum 1G carbonized around each of wells 12 and 14in the area within the boundaries alessia carbonization has beeneffected `as shown, the stratum may be produced further by igni-ting theshaile around either well and feeding combustionsupporting gas, such asair,

to the combustion zone to move the combustion front thru the stratum tothe other well. This drive may be effected by either inverse or directinjection of air. The combustion front goes thru the `fractures in theimpermeable uncarbonized section so vas to produce hydrocarbons from theshale adjacent the fractures.

In ya. further embodiment of the invention, fractures 40 in FIGURE 4 maybe rendered conductive by introducing thereto particulate conductivematerial. Suchl conductive materialincluding powdered metals isdisclosed in the prior art such asin the patent to Dixon2,818,ll8 issuedDecember 31, 1957. After the conductive Inlaterial -is disposed in .thefractures, current is passed between electrodes in wells 12 and 14, asshown in FIGURE 2, so xas to heat the shale adjacent the fractureswhereby the hot shale becomes conductive and oil is produced from theshale. The passage lof current thru the fractures is continued so as toelectrocanbonize shale deeper into the formation above and below thefractures and thereby expand the carbonized zone. Fluids produced duringpreceding steps are recovered thru either Well or in the mannerillustrated in FIGURE 5` where well 14 represents a welll in a ring ofwells and well 12 is a central well. Of course, a combustion front canbe passed thru the carbonized shaile following the preceding sequence ofsteps.

In any of lthe figures of the drawing, Well 14 may represent a wvell ina ring of wells surrounding welll 12. FIG- URE 5 illustrates such `awell pattern wherein gas, such as air, for supporting combustion isinjected thru line 211 into a distributing ring 15 Yfor injection intowells 14 thru feed lines -17 extending from ring 15 to each weil. Theproduction is recovered from well 12 thru line 19 and passed to productseparation means not shown. It is also Ifeasible to inject ythecombustion-supporting gas thru line -19 and recover production thruwells 14 by means of lines 17, ring 15 and line 21.

lCertain modifications of the invention will become apparent to thoseskilled in the art `and the illustrative details disclosed are not to beconstrued as imposing unnecessary limitations Ion the invention.`

'I claim: Y

1. A process for producing oil shale in situ which comprises heating -asection of said shale around a production well therein to render saidsection electrically conductive;

while the section is hot, electrocarbonizing said section so as todistill hydrocarbons therefrom and lproduce hot permeable coke thereinat a combustion supporting ternperature; continuing theelectrocarbonizing step until shale `in said section is fracturedradially outwardly from the carbonized section; thereafter injecting afree-oXygen-containing gas into an offset injectionwell from which atleast one fracture leads to said section so that `said gas passes intosaid section and ignites said hot carbon; continuing the combustion;land recovering fluids produced by the electrocarbonizing step and thecombustion step thru said production well.

2. The process of claim 1 wherein said shale is fractured radiallyoutwardly to said injection well from the carbonized section byexpansion of said section during the electrocarbonizing step.V

3. The process of claim 2 wherein a ring of injection wells surroundsaid production well within the fractured area and said gas is injectedthru said ring of wells.

4. The process of claim 1 wherein at least one of the flow rate of saidgas `and the concentration of O2 therein is regulated so as to move lacombustion front thru said fractures toward said injection well.

5. A process compris-ing heating a dry, nonconducting oil shale to asufficiently high temperature to render same electrically conductive;electrocarbonizing a section of the vheated shale around a first Welltherein; continuing the electrocarbonizing step until said shale isfractured radially outwardly from the carbonized section by expansion ofsaid section; electrocar-bonizing a second section of said shale aroundan offset well therein; continuing the electrocarbonizing step until theshale surrounding the second carbonized section is also fractured torform a ow path with aforesaid fractures between the wells; thereafterignitng and moving a combustion front thru said shaleV between saidwells; and recovering fluids produced 'by the electrocarbonization andcombustion steps.

6i. The process of claim 5 wherein said combustion front is initiatedaround one of said Wells by injecting air into same and moving saidfront by direct drive to the opposite well.

7. The process of claim 5 wherein the hot carbon in the carbonizedsection `around one Well is cooled below combustion supportingtemperature and air is injected thru said one well so that it passes tothe hot carbon in the carbonized section around the opposite well,thereby igniting saine Iand moving said combustion front by inversedrive to said one well.

8. A process -for producing an `oil shale in situ which compriseselectrocarbonizing a substantial section of said shale `around a firstwell therein so as to distiill hydrocarbons therefrom and produce hotpermeable coke therein atcombustion supporting temperature; continuingthe electrocarbonizing step until fractures extending radially outwardlyfrom said section are produced by expansion of said section; providing-a second well in said shale within the fractured yarea; injectingfree-oxygen-containing gas into the hot coke so as to ignite same andestablish in situ combustion; `continuing the injection of said gas soas to move a combustion zone thru said shale to said second well; andrecovering fluids produced by the carbonization and combustion steps.

9. The process `of claim 8 wherein air is injected thru said first wellso `as to move said combustion front by direct drive.

10. The process of claim 8 wherein air is injected thru said second wellso las to move said combustion `front by inverse drive.

ll. A process comprising electrocarbonizing a section of shale around laiirst well; continuing the electrocarbonizing step until said shale isfractured radially outwardly from the carbonized section by expansion ofsaid section during the'electrocarbonizing step; electrocarbonizing aVsecond section of said shale around an offset well therein; continuingthe ellectrocarbonizing step until the shale surrounding thesecondwc'arbonized section is also fractured to form a flow path withaforesaid fractures between the wells; thereafter depositing particulateconductive material in said fractures; and passing current between anelectrode in said first well 'and an electrode in said second well thruand along said fractures solas to heat the adjacent shale whereby thehot shale becomes conductive; continuing the passage of current toelectrocarbonize the shale adjacent the fractures |and to expand thecarbonized Zone; and recovering produced fluids from one of said wells.

References Cited in the file of this patent UNITED STATES PATENTS2,795,279 Sarapu June ll, 1957 2,818,118 Dixon Dec. 3l, 1957 2,967,052Crawford Jan. 3, 1961k OTHER REFERENCES Mining Congress Journal October1949, page 57.

1. A PROCESS FOR PRODUCING OIL SHALE IN SITU WHICH COMPRISES HEATING ASECTION OF SAID SHALE AROUND A PRODUCTION WELL THERIEN TO RENDER SAIDSECTION ELECTRICALLY CONDUCTIVE; WHILE THE SECTION IS HOT,ELECTROCARBONIZING SAID SECTION SO AS TO DISTILL HYDROCARBONS THEREFROMAND PRODUCE HOT PERMEABLE COKE THEREIN AT A COMBUSTION SUPPORTINGTEMPERATURE; CONTAINUING THE ELECTROCARBONIZING STEP UNTIL SHALE IN SAIDSECTION IS FRACTURED RADIALLY OUTWARDLY FROM THE CARBONIZED SECTION;THEREAFTER INJECTING A FREE-OXYGEN-CONTAINING GAS INTO AN OFFSETINJDECTION WELL FROM WHICH AT LEAST ONE FRACTURE LEADS TO SAID SECTIONSO THAT SAID GAS PASSES INTO SAID SECTION AND IGNITES SAID HOT CARBON;CONTINUING THE COMBUSTION; AND RECOVERING FLUIDS PRODUCED BY THEELECTROCARBONIZING STEP AND THE COMBUSTION STEP THRU SAID PRODUCTIONWELL.